The blaze broke out in plantations near Nelson yesterday and has burned through more than 2,000 hectares of plantation and heathland and into the Lower Glenelg National Park.

Victoria's Fire Services Commissioner Craig Lapsley says the fire has become so large that it will not be possible to bring it under control tonight, despite cooler conditions halting the fire's progress.

"It is not threatening any settlement, the highway has been reopened," he said.

"It's burning within the park, has got significant resources both firefighting crews and aircraft, and it will require quite a lot of work to bring that to a controlled situation."

The CFA says the fire is not a threat to lives or property.

"Crews have been working all night to do the back-burning operations," the CFA's Alen Slijepcevik said.

On the other side of the state, a fire burning in a remote alpine area near Swifts Creek, north of Lakes Entrance in the Gippsland region, has been contained.

The CFA says a cool change has helped slow the fires' progress.

A small fire at Red Hill on the Mornington Peninsula which started in the early afternoon has also been contained.

Temperatures in much of the south-west have now dropped to the mid-teens, and the cool change has also swept through Melbourne.

But the weather bureau warned there would be little relief in the state's north - temperatures there were again forecast to reach the mid-40s.

Website failure

After more than 60 fires broke out across the state yesterday, thousands tried unsuccessfully to log onto the CFA's website for the latest fire warnings.

Mr Lapsley says he was disappointed the website had not coped with demand.

"At one stage, we had 700 calls or touches on the website per second - 700 per second.," he said.

"We have spent time testing our capability, running scenarios, but certainly the workload is above that of what we expected, so there's some very key lessons learnt that we will take forward and fix as a matter of priority."

But it was not just the website that did not deliver yesterday.

The CFA's 'Fire Ready' smartphone app also had problems, including failing to show accurate warnings.

Mr Lapsley conceded it was slow, and that was largely because the app is linked to the website.

The CFA says their website is now up and running, but they say if there is another failure, people can still get information from the CFA's Facebook and Twitter pages.